An electrode of a battery is made by the following processes; coating a paste compound made by compounding an active material, a conductive additive, a binder and the like with a diluent on a surface of a collector made of aluminum, copper, or the like, drying, and roll pressing.
As stated above, the compound is made from multiple materials such as the active material, the binder and the like. Unfortunately, if the compound is coated on the collector such that the multiple materials are not mixed evenly in the compound, variation in the electrode performance increases and dendrites are generated. Therefore, it is necessary to detect whether the compound is coated on the collector such that the multiple materials are scattered evenly in the compound or not (to detect an evenness of the compound).
Patent Literature 1 discloses that the evenness of the compound is evaluated by irradiating the electrode with x-ray, and calculating a mass per unit area of each of multiple parts of the compound from the permeation volume of the x-ray.
However, in Patent Literature 1, the evenness of the compound is evaluated on the basis of one measurement value, namely only the mass per unit area of the compound calculated from the permeation volume of the x-ray, so that when the compound is judged as uneven, it is impossible to identify whether the unevenness of the compound is caused by a change of a thickness of the compound or by a change of a mixing ratio of the multiple materials in the compound.
Moreover, a measurement apparatus using the x-ray has a poor resolution and such apparatus has a disadvantage in a quality control of the electrode, because the performance of the electrode depends on the evenness of the compound.    [Patent Literature 1] JP 2006-147338 A